The invention relates to the technical field of instruments producing charged particles beams in an energy range from 1 eV/charge to several 1012 eV/q.
Such types of instruments have applications in many fields, depending on the charge, the mass, and the kinetic energy of accelerated particles:                equipment of the particle accelerators        ion implantation (surface treatment, etc. . . . )        medical field (hadron therapy, radioisotope production, nanodrugs . . . )        vacuum deposition        micro-etching        ion propulsion for spacecrafts        acceleration mass spectrometer for sample analysis,        dating.        
The invention relates more particularly to the modulation of the intensity (or current or flow of particles) of the charged particle beam produced in order to modulate the impact thereof on the target sample and to be able to vary the possible uses of same instrument.
At present, the charged particle beams can be current modulated in different ways, specifically:                by varying the intensity of the charged particle source        by collimating the beam using removable mechanical parts (e.g. slots system, iris)        by pulsing the beam with various duty cycles.        
The various techniques mentioned above, however, raise many technical problems:                pulsed beams, for instance, cannot be used in all the applications of the charged particle beams,        the setting of the intensity of the charged particle source and the use of mechanically removable collimators do not meet the reactivity constraints required by some applications.        
In the example of the document U.S. Pat. No. 8,896,238, the current of a beam from an ion source generating a curved ion beam within a specific accelerator of the cyclotron type can be modulated. The intensity of the beam is modulated using a Dee electrode connected to a high frequency generator which applies to the Dee electrode an alternating high voltage the amplitude of which can be modulated by a regulator. The ions are accelerated between the Dee electrode and a counter-electrode connected to the ground, through a gap and define, because of the application of voltages of different amplitudes to the Dee electrode, circular paths having different radii. A solid screen spaced apart from the counter-electrode defines with the latter a space for the passage of ions following the trajectory of a curvature exceeding a critical value, and defines an obstacle for the ions the curvature of which is below same critical value. Modulating the amplitude of the voltage applied to the Dee electrode which modifies the various trajectories of the ions, combined with the presence of the screen, makes it possible to modulate the number of ions and thus the current finally emitted by the source.
However, this device is specific to the charged particles having curved trajectories emitted by a source of cyclotron and cannot be applied to a device emitting a linear charged particle beam.
The document U.S. Pat. No. 3,286,123 relates to an apparatus emitting a linear particle beam. In this apparatus, under the effect of a perforated electrode, a deflection system and multiple lenses distributed along the axis of emission thereof, and the presence of a deflector, the charged particle beam is deflected from its original path according to variable profiles depending on the position and focal length of the lenses and some may be collected by a collector placed perpendicularly to the emission axis of the particles. The applications of this device however, are not compatible with those aimed at by the invention, since the charged particle beam is definitely deflected from its original axis and not recoverable at a given fixed location.
Other devices generating linear charged particles beams and provided with modulation means are known but this modulation is performed on the energy of the beam and not on the current (the amount) of particles:                the document EP 2592642 relates to a device emitting a charged particle beam comprising a succession of octupole elements (302, 304, 306, 308) capable of being the seat of dipole, quadrupole and sextupole excitations, with the first two elements enabling a dispersion in height and energy of the beam, with the two core elements being separated by a collimator provided with a slot-shaped orifice letting a portion of particles having a given energy through, and intercepting the others. This device thus makes it possible to modulate the energy of the charged particle beam, but not the intensity of the exiting beam which remains substantially the same,        besides, the document U.S. Pat. No. 8,039,822 relates to a charged particle therapy apparatus comprising an accelerator for generating a charged particles beam, with a passive energy modulator comprising an absorbent element and a control unit. The control unit is adapted to switch between an active adjustment of the energy contained in the accelerator and a modulation of the passive energy by the energy modulator, in order to modify the energy of the charged particle beam from a high energy level to a low energy level, stepwise. In particular, this results in shortening downtimes when switching between energy levels but still not the possibility of modulating the intensity of the exiting beam.        
The document U.S. Pat. No. 9,224,569 discloses a high brightness ion source with a gas chamber which includes various compartments, each one being provided with a different gas. An electron beam is caused to selectively pass through one of the compartments to provide ions of a certain kind for processing a sample, using deflection plates. It is possible to easily change the species of ions provided by directing the electrons through other compartments containing a different kind of gas in order to process a sample with ions of another kind. If the nature of the ions generated is quickly and easily changed, the number of ion species is reduced to the number of compartments of the gas chamber, and the possible different beam intensities of the various possible ions are also reduced to the number of compartments in the chamber. This system does not allow a continuous change in the intensity of the beam supplied.
So, no satisfactory solution has yet been found for modulating in intensity, continuously, the charged particle beam emitted by a source supplying a linear accelerator.